Method and apparatus for manufacture of insulated wire and cables for electrical purposes



y 1950 D. c. HANCOCK ETAL 2,509,432

METHOD AND APPARATUS FOR MANUFACTURE OF INSULATED WIRE AND CABLES FOR ELECTRICAL PURPOSES 3 Sheets-Sheet l Filed Feb. 15, 1947 May 30, 1950 D. c. HANCOCK ETAL 2,509,432

METHOD AND APPARATUS FOR MANUFACTURE OF INSULATED LES FOR ELECTRICAL PURPOSES WIRE ANDCAB Filed Feb. 15, 1947 3 Sheets-Sheet .2

A Home y May 30, 1950 D. c. HANCOCK ETAL 2,509,432 METHOD AND APPARATUS FOR MANUFACTURE INSULATED WIRE AND CABLES FOR ELECTRICAL POSES Filed Feb. 15, 1947 3 Sheets-Sheet 3 Attorney Patented May 30, 1950 TUBE OF INSULATED WIRE AND CABLES FOR ELECTRICAL PURPOSES Douglas Charles Hancock, North Wembley, and Hermann Richard Lorch, London, England,assignors to British Insulated Callenders Cables Limited, London, England, a British company Application February 15, 1947, Serial No. 728,880

In Great Britain March 7, 1946 7 Claims.

1 This invention is concerned with the manufacture of insulated wire and cables of the kind in which the insulating material is a thermoplastic substance. It relates particularly to the case where insulating material is applied in a any bubbles of gas which exist in the injected material are reduced in size by compression and maintained under compression whilst the material sets to form a solid dielectric body surroundmg the conductor and insulating it.

2 Most conveniently support to the mould is given by a fluid medium under super-atmospheric pressure within a pressure resistant casing surrounding the mould for an appropriate distance 5 from its formation point. substantial radial thickness. The method of The extruded metal tube forming the mould manufacture provides against disadvantageous m y be l on the conductor to f a p effects which may result from shrinkage of mant metal s a h f r it ay be s pp d terial during cooling and against the existence the insulerted e d i either immediately of bubbles of gas in the conductor covering of a lthas served Its pu p a a ou d or su size such as to affect seriously or even appreciably l y; Wh e mould 1S OI a t p a the electrical properties of the covering. 3: l ze i g s gg 3 3:25; In the improved method of manufacture of ina e i sulated wire and cables we apply features of the 1t may e me than Phmner than would technique of injection moulding of thermoplastic 15 n to P If It r l'equlred to form a Sheath materials. In the injection moulding of such ma- 5313212 12 figgt gg gg siing out the impl ved terial, th mouldin material, in a fluid s ate and j r under g pressufie is injected throng; an method of manufacture includes an extrusion dejection orifice or nozzle into the mould and al- Vice f the productien of metal tubing by lowed to set under the high injection pressure j e plastle {netalfihrougl} an annular m before being ejected from the mou1d In accord sion orifice. Th s device may be a metal extrusion ance with the present invention the insulated oovpress or a eentmfleus Fletel extruelen m ering is applied to the conductor by an injection "5 extrusm; g formetdr W moulding process of a continuous nature. In this 313 2:233: :3 %:5 f $5 523: g gg g g g fi ggg g gfigg g f szi ifi the invention this point is tubular and carried mould of which the wall travels forward contintubular point holder which, contains an ually at the speed of the conductor. The tubular figigg e g ggg ffigfig gg ii pg ggz ggfif l ggf $315 31 it ufi'ifi wil i by it xiiuiti fifiilfl 3o duster to be covered: The inner e homer As the mould travels forward, it is filled with the Supports correspongmgly apertured' linger pomt covering material in a fluid state and under high 25 2 153 3 ?ifigzi g g ggzg fifigfi f fi ggg sg pressure by contiguous mJectmn mouldmg covering material in a fluid state is injected into process mould 1s suppmjted externally by 35 the clearance between the conductor emerging surrounding it for an appropriate distance from from the passage through the inn point and the its formation point with fluid medium under wall of the metal tube extruded around it Comatmospheric pressure and heat is abstracted from bined with this extrusion press or extrusion the pressure )t length of to 9 chine is some pressure means for the supply of and set e magma 'f matenal therem' 40 fluid covering material to the interior of the tubu- An appmpnate f 15 the dlstafnce between lar point holder leading to the injection orifice. the metal extrusion d e and the point at whlch This pressure means may be of the hydraulic the mleeted flmd solldlfiesour Improved press, the reciprocating or rotary screw type commethod of manufacturer as the Wlre and the filled bined with a heating arrangement to ensure that mould move forward, the material in the mould is material of the right fluidit and pressure is cooled to its setting point whilst still under the plied at the injection ific high p s e exerted y the following material- On the delivery side of the extrusion device is Thus the risk 0f void formation by shrinkage iS prawn-13] the means for supporting an appror du ed y t f l w-up movement of fl priate length of the extruded metal tube exterterial from the hotter parts of the mould and nally against the high internal pressure exerted by the insulating material and for abstracting heat from the pressure supported length of mould to cool and set the injection moulded material therein. Preferably this means comprises a pressure-resistant tube which is coupled at one end in a fluid-tight manner to the outer die or matrix of the metal extrusion device and is supplied with fluid under super-atmospheric pressure which serves as a cooling medium causing the injected material to set within a reasonably short distance of the injection moulding point. Preferably the pressure resistant tube is of such a construction that it serves to maintain the extruded metal tube substantially in alignment with the extrusion orifice until the injected material has set. This assists in preventing lateral displacement of the conductor during the setting process.

The choice of the metal for .the tubular mould is guided by the properties of the insulating material to be injected into it, there being an appropriate coordination of the temperature of softening of this material with the extrusion temperature of the metal. For instance, where the conductor is to be insulated with polyethylene, an appropriate metal would be lead or a lead alloy since the extrusion temperature for such metal would not be less than the temperature at which polyethylene becomes sufficiently fluid for injection moulding. In the case of an insulating material of which the softening and moulding ternperatures are too high ior the mould to be of lead or a lead alloy, resort may be had to a mould of aluminium.

To enable the invention to be more fully understood and to be readily put into practice, an example of apparatus for carrying out the improved method or manufacture will now be described in detail and with the aid of the accompanying drawings, wherein Figure 1 is a plant diagram,

Figure 2 is a sectional elevation of the apparatus for injection moulding insulating material on a conductor,

Figure 3 is a plan of the apparatus shown in Figure 2, and

Figure 4 is a cross-section taken on the line IV'IV in Figure 2 but drawn to a larger scale.

The plant shown in the drawings is one that issuitable for the manufacture of a single core cable having a dielectric of a low melting point plastic, such as polyethylene, enclosed in a lead sheath. As is shown in Figure 1, it comprises a lead press l for extruding a tube of lead or "lead alloy around the conductor as it passes through the press, a second press 2 for forcing liquid plastic into the space between the conductor and the lead tube surrounding it, a cooling tube 3 on the delivery side of the lead press "and hydraulic pumping apparatus 4 for supplying the tube 3 with a pressure fluid which serves both to support the extruded tube against the internal pressure of the liquid plastic and to abstract heat from the tube and the injected plastic and bring about a gradual setting of the plastic.

The construction of the lead press I is clearly shown in Figures 2 and 3 of the drawings. It consists of a vertical container ll having axially aligned lateral openings in its cylindrical wall. In one of these is secured a die block l2 having a horizontally extending stepped cylindrical passage l3 the inner and smaller end of which opens into the container and forms the extrusion chamber. In the outer and larger end of the passage i3 is a disc which is centrally apertured to form'an outer die or matrix [4 and is held against the step by a tubular die holder 15 secured by studs and nuts to the die block l2. Cooperatin with this outer die 14 is an inner die or point it carried on the end of a point holder I! which passes through the other opening in the wall of the container and a point holder support I 3 housed in the outer end thereof, to be held in place longitudinally by a locking ring is which screws into the point holder support [8 and clamps the inner face of a collar 20 on the point holder against a seating in the support, and angularly by a key I I9. At its front end the point and point holder are supported by a spider 2!. The container is fitted with a ram 22 which is acted upon by the hydraulic rarn of the press (shown in Figure 1 only) to force lead in a plastic state out of the container ll into the passage l3 in the die block l2 and through the annular orifice 23 between the matrix M and the external surface of the hollow point It to form a lead tube.

The point It and the point holder I! are tubular. Within this point holder H is an inner point holder 24 terminating at its forward end in a combined inner die and spider 2,5 which cooperates with the tubular point l6 toiorm an annular injection orifice. The inner die and holder are apertured and serve toconvey the con ductor 26 through the outer point holder and position it centrally with respect to the extruded metal tube 2? (Figure 4). At its rear endthe inner point holder is supported by a part 28that is a sliding fit in the outer point holder If! and its position with respect to the latteris adjustabl controlled in an axial direction by means of a flanged bush 29 which is located between the part 28 and a flange 30 on the extremity of the holder and screws in the internally screw threaded rear end of the outer'p'cint holder 11. Rotation of the inner point holder is prevented by a pin l29 working in a groove in the part 2t. The outer point holder I! has at its rear end a lateral feed inlet 3| by which'the material to be injected into the lead tube is fed under high pressure by means of the hydraulic press 2 (shown diagrammatically in Figure l') to which it is connected by a pipe line 32. The pre'ss'is supplied through a'pipe line '33 from 'a' heated feed vessel 35in which the plastic 'is'brought to a liquid condition and'fromwhich it is expelled by compressed nitrogen, the now being controlled by a gas valve l'34andan outlet valve'l33.

The cooling'tube 3, which may have a length of about six feetor more, isjointed at itsrear end'to'the outer die land at intervals along'its length is held insupports3'5-secured to the'u'pper face of a T-section girder 35 forming an elongated table. This table' is supported at its front end by'a pivot 31 and at its rear-end;through--the rear end of the cooling tube-by the die 14. permits the cooling tube to' follow, without-bending-any lateral movement ofthe-die l'4,'wl1ich in accordance with general practice is laterally adjustable on-its seating. The -cooling tube-isexternally screw threaded at each-end and on these screw threaded portions 68a, 381) are screwed jackets 39a, 39b and pairs of rings llla, 42b which serve to lock the jackets onthe tube and, with the aid of packing washers lla, Mb, .to seal the joints between the jackets and tube. At these points the cooling tube is apertured toplace its interior in communication withthe interiorof the jackets. The jacket 3% on the front end of the tube is fitted with aconnecting tube142b through which oil under pressure can be fed to the tube. A second connecting tube-43b serves to connect with a pressure gauge 44b. The other jacket 39a has a single connecting tube 342a through which oil can flow fromthe coolingtube.

On the extremity of thescrewed rear end 38a of the tube 3 is a connecting sleeve 45 which screws into the internally screw threaded wall of a recess in the outer face of the die It and makes a fluid-tight joint between the cooling tube and the die. On the front end of. the tube is a sleeve 46 whose bore is such that it is a sliding fit on the lead sheathed conductor. On the end of this sleeve is fitted an outlet tank 51 having an outlet it for the issuing cable in alignment with the sleet/ed t. Any pressure fluid leaking past the sleeve 45 is collected in the tank. ,The outlet is fitted with a felt wiping pad 49. V

The hydraulic pumping apparatus, designated 4, comprises a motor driven pump which draws oil from a reservoir 52 and delivers it at high presure to two pressure reducing valves 53a.

531). From the valve, 53a oil at an .appropriate pressure is conveyed through a pipe line ti l to the hydraulic cylinder 55 of the press 2, suitable control valves 56 and 53' and a gauge at being inserted in the line. From the reducing valve 53b oil is fed at a suitable pressure controlledby a by-pass valve 59, through a pipe line 56 to the cooling tube 3. From the inlet 221) the pressure fluid flows along the clearance between the extruded lead tube and the wall of the cooling tube to the outlet 42a, abstracting heat from the lead tube and the plastic with which it is filled. From the outlet 42a, it is returned through a pipe line 61, fitted with a pressure gauge 52 and a control valve 63, which controls the rate of flow, to the reservoir 52 where it is cooled in any convenient manner such as by a refrigerating coil. Oil collecting in the outlet tank ll is drainedoff into, a vessel 64.

In operation the conductor 26 is drawn off from a supply reel 65 and fed into the lead press through the inner point holder 24, pressure is exerted by the ram 22 to force plastic lead through the extrusion orifice 23 to form a lead tube 21 which is pushed forward along the cooling tube, and pressure is exerted by the ram of the plastic press 2 to force liquid plastic along the annular passage between the inner and outer point holders and through the annular injection orifice into the space between the conductor and the lead tube. The internal pressure exerted on the lead tube is counteracted to a desired degree by the oil supplied under pressure to the cooling tube, which has access to the exterior of the extruded lead tube immediately it leaves the throat of the outer die I l. The rate of flow of oil, which is controlled independently of the pressure and its inlet temperature are so adjusted that the injected insulating fluid is set before the product emerges from the cooling tube to be taken up on a suitable take-up device shown diagrammatically at 66.

The radial clearance between the extruded tube and the wall of the cooling tube, which in this case forms the cable sheath, may be of the order of ten thousandths of an inch, so that the lead tube is centred with sufficient accuracy in the cooling tube. The surrounding oil film serves as a lubricant. In such a case the cooling tube may be internally fluted, for example, as shown in Figure 4;, to ensure that a flow of oil sufiicient for cooling can be maintained without difiiculty. In this figure, the injected insulating material is shown as still fluid and is designated 61, the cooling oil surrounding the lead tube 21 being designated 68.

It will be understood that the lead press will be provided with heating or cooling means for bringing the lead to an appropriate extrusion temperature Such means are well knownhow-r ever and need not be described. Naturally other known types of extrusion apparatus may be em,- ployed instead of aram operated press'shown. The second press will also be appropriately heated to maintain the insulating material in a fluid state, and the pipe lines for conveying the material from the supply tank to the press and from the tank to the outer point holder will be heated, as by a steam jacket, for instance.

What We claim as our invention is:

1. A method of manufacturing a conductor insulated with thermoplastic material, which comprises extruding a metal tube around the conductor to form a continuous mould enclosing the conductor with a large clearance between the conductor and the wall of the mold, filling the mould, as it is formed, by lcontiuously injecting the insulating material in a temporarily fluid state andunder high pressure into it, reinforcing the mould against internal pressure for a distance from its formation point by surrounding it with a fluid medium under super-atmospheric pressure, and abstracting heat from the pressuresupported mould to cool and set the injected material therein.

2. A method of manufacturing a conductor insulated with thermoplastic material, which comprises extruding a metal tube around the conductor to form a continuous mould enclosing the conductor with a large clearance between the conductor and the wall of the mould, filling the mould, as it is formed, by continuously injecting the insulating material in a temporarily fluid state and under high pressure into it, surrounding the mould for a distance from its formation point with a fluid medium under super-atmos pheric pressure to support it externally, and causing said fluid pressure medium to flow in the form of a thin annular stream surrounding the mould in a general direction counter to the direction of travel of the mould, whereby to abstract heat from the pressure-supported mould so as gradually to cool and set the injected material in the pressure-supported part of the mould.

3. A method of manufacturing a conductor insulated with thermoplastic material, which comprises extruding a metal tube around the conductor to form a continuous mould enclosing the conductor with a large clearance between the conductor and the wall of the mould, filling the mould, as it is formed, by continuously injecting the insulating material in a temporarily fluid state and under high pressure into it and abstracting heat from the mould to cool and set the insulating material therein by flowing an externally rigidly supported, thin annular film of oil under superatmospheric pressure over the surface of the mould.

4. Apparatusfor injection moulding a covering of thermoplastic insulating material on a conductor, comprising an extrusion device for the production of metal tubing having a laterally adjustable matrix and a point which co-operate to form an annular extrusion orifice, a tubular point holder for carrying the point, an inner point holder located within the tubular point holder and apertured for the through passage of the conductor to be covered, and a correspondingly apertured inner point supported by the inner point holder and co-operating with the tubular point to form an annular injection orifice for the injection of the thermoplastic covering material in a temporarily fluid state and under high pressure into'rthe metal tubing, combination wither-tubularpressure-resistant casing forreceiving the. extruded metal tube issuing from the :annular extrusion orifice, an (elongated table :for supporting saidtubular casing, a pivotal support ior said table at the front end thereof, means for making afluid-tight joint between the matrix and the rear end :of the tubular casing, means ior :supporting the rearend of the table from the rear end of the tubular casing coupled to the matrix and means for supplying said tubular casing with fluid under pressure for supportin the extruded metal tube externally as it passes therethrough.

5. A method of manufacturing a conductor insulated with thermoplastic material, which comprises-extrudinga metal tube around the conductor to form-a continuous mould enclosing the conductor with alarge clearance between the-conductor and the wall of the mould filling the mould, as it is tormed, by continuously'injecting the insulating material in .a temporarily fluid state and under high pressure into it, .cool- 'ing the sheath to set the injected material therein and reinforcing it against internalpressure by-surrounding it-by fluid under super-atmospheric pressure and until the injected material has set maintaining the conductor and the sheath insubstantialalignment with one another by maintaining-the conductor under tension and applying continuous close support to the sheath.

6. A method of manufacturing a conductor insulated with thermoplastic material, which com-prisesextruding a metal tube around the conductor to form a, continuous mould enclosing the conductor with a large clearance between the conductor and the wall of the mould, filling the-mould, as-it is formed, by continuously injectingthe insulating material in atemporarily fluid state and under highpressurein-to it, cooling thesheath to set the injected material and until theinjected material therein has set reinforcin the sheath against internal pressure'by 8 surrounding byfluid under super-atmospheric pressure while. continuously positively limiting movement in lateral directions.

'7. Apparatus for injection moulding a. coveringrof thermoplastic -material on a conductor, comprising aniextrusion device for the production- 0f metal tubing having a laterally ad-justable matrix and a point which cooperate to form an annular extrusion orifice, a tubular point holder tor carrying the :point, means for guiding the conductor to be covered into and through the tubular point holder and its point, and means for supplying-thermoplastic material in :a temporarily fluid state and under high pressure to the interior of-said point holder, incombination with a tubular pressure-resistant casing for reoeivi-ng the extruded metal tube issuing from the extrusion orifice, an elongated table for supporting said tubular casing, :a pivotal support for said table at the *frontend thereof, means for makin a :fiuid-tight joint between the-matrix-and the rear end of the tubularcasing, means for supporting the rear end of the table =fromthe rear end-ofthe tubular casing ecu-pied to the matrix, and means for supplying said tubular: casing with fluid under pressure for supporting the extruded metal tube externally asit passed therethrough.

CHARLES HANCOCK.

RICHARD LORCH.

KEEER'ENCES CITED "The following references are of record in the fileof this patent: .UNI'IED STATES PATENTS Number Name Date 1 710385 ;Kiyley -.p July .22, 1930 2,121,966 Jacobson June 28, 1933 1371309 :Rineer .Mar. 20., 1945 12,384,224 Williams Sept. 4, 1945 12,401,,642 Hiltner et a1. .June 4, 1946 

